This invention relates to new methods and apparatuses for purification of water and wastewater with immobilized living cell bioreactor systems. In particular, the bioreactor systems may remove organic impurities, nitrogen, phosphorus and biodegradable solids.
In general, a biological wastewater treatment system usually consists of three essential components:
1. Living Biomass:
A wide variety of microorganisms have been found to remove different target pollutants. In order to maximize the efficiency of the biological treatment, it is necessary to select proper microbes depending on the types of pollutants to be treated. The acclimatization of microbial consortia for particular purposes is well known in the art. Some microbial species which have been characterized are available from recognized depositories of biological materials.
2. Biomass Handling:
A bioreactor may achieve high efficiency when it supports the living biomass to grow healthily in high density and retain them properly in the bioreactor under various adverse conditions. Biomass handling methods that are used in water and wastewater treatment may be generally classified into two general categories: suspended and immobilized biomass.
Suspended biomass systems have been widely used in activated sludge (xe2x80x9cASxe2x80x9d) systems and part of rotating biological contactor (xe2x80x9cRBCxe2x80x9d) systems, however, the inherent limitations in these systems have driven continuous research in immobilized biomass methodology. Immobilization of living microbial cells as a means of handling biomass has gained increasing application, especially for biological nutrient removal.
Two predominant immobilization methods are a xe2x80x98biofilmxe2x80x99, in which the microorganisms are attached to solid surfaces, and an xe2x80x98entrapped biomassxe2x80x99, in which the microorganisms are held within micropores in the support material. The attached biofilm has been widely used in RBCs and trickling filters. In this method, the biomass is immobilized through adsorption and interactions between the microbial cells and the surfaces of supporting material. The immobilization of biomass using this method may be relatively weak, and the biomass periodically sloughs off the surface of the supporting material. Entrapment methods include the use of a matrix of calcium alginate gel. The major limitations of this immobilization method are that it is impractical to use in a commercial scale, as the beads are expensive and are mechanically or chemically instable. Poor mass transfer within the beads also greatly limits its application in large scale.
A porous ceramic immobilization material has been developed for large-scale applications. However, in practice, it has been found that the total suspended solids (xe2x80x9cTSSxe2x80x9d) and the growth of microbial cells easily clog the micropores. As the micropores became clogged, mass transfer and headloss problems occur, similar to problems which affect calcium alginate gel systems, and only a thin layer of biofilm can grow on the surface of the ceramic immobilization material.
3. Hydraulics and Mass Transfer:
A wastewater treatment system is only effective if the living biomass is provided with sufficient metabolic substrates and the waste metabolites are removed properly from the living biomass.
Obviously, the performance, flexibility and reliability of a biological wastewater treatment system are strongly dependent upon the effectiveness of the three components mentioned above. The main types of biological systems in wide use today, activated sludge (AS), rotating biological contactor (RBC) and conventional biofilters (or trickling filters) referred to above, suffer from shortcomings in one or more components mentioned above, which have been well documented in the literature.
Conventional biological wastewater treatment systems typically require a primary clarifier or sedimentation step, including the application of flocculating or coagulating chemicals, prior to biotreatment in order to mitigate the shortcomings of the prior art. This step is conventionally necessary to reduce the level of suspended solids so the biotreatment system does not become overloaded or clogged.
The biological conversion of complex or insoluble compounds containing phosphorus (P) or nitrogen (N) into simply P or N, requires a series of biochemical reactions carried out by several different microbial consortia. These organisms grow under different conditions, have substantially different growth rates, and therefore compete differently for substrates, carbon and energy sources. Thus, any biological treatment system will only be effective if it can grow different desired microbial consortia, each to a high density and in a favorable environment.
Both phosphorus and nitrogenous compounds are encountered in wastewater in two general formsxe2x80x94inorganic and organic forms, which together make up total phosphorus (TP) or total nitrogen (TN). Complex phosphorus and nitrogenous compounds are found in soluble and insoluble states, and usually need to be converted into simple form such as orthophosphate or ammonia before use by most microorganisms.
Facultative anaerobic processes are found to be most effective for converting complex P or N into orthophosphate or ammonia. These processes involves various hydrolyzing enzymes from acclimatized microorganisms. However, these type of microorganisms usually grow slowly, are less competitive than other microorganisms and require certain special conditions.
After biological conversion, most of the N and P are in solution, and only a portion is assimilated into the biomass. Often, the ultimate goal is to reduce the N and P compounds from the water and wastewater to specified levels to meet discharge or re-use requirements. Several biological processes for removal of the N or P compounds are well known in the art. Such conventional systems typically involve suspended growth systems or sludge wasting methods.
To biologically remove soluble P, there is need for a selection system that allows for growth and retention of the P-removal microbial consortia in the bioreactor system in a reasonable concentration. This biomass may then absorb the PO4xe2x80x94P in relatively high concentrations in its microbial cells. After reaching the maximum capacity under favorable conditions, the biomass is typically removed from the system and disposed of as waste sludge before it can release the absorbed P into the solution again. Although this treatment method may remove PO4xe2x80x94P, the P removal biomass in the process varies considerably with the wastewater characteristics and operation, and it is very difficult to control. The disposal of significant amount of wasted biomass, or sludge, is also a great burden.
The chemistry of nitrogen is more complex because N can exist in seven oxidation states. Although many species of bacteria are able to change the oxidation states of N, they usually grow slowly and are much less competitive compared to heterotrophs. In addition, the biochemical processes for conversion of N are usually kinetic limiting processes. To improve the efficiency of these biological processes, it is desirable to selectively grow the desired species efficiently and in high density in the bioreactor and it is further desirable to provide the favorable growth conditions for these microorganisms to maximize N removal efficiency.
The present invention comprises integrated biological processes and novel bioreactor systems. In particular, this invention comprises a series of bioreactor systems using integrated biotreatment processes for the removal of organic material or BOD, suspended solids (xe2x80x9cSS or TSSxe2x80x9d), N and P from water and wastewater.
In general terms, the invention comprises a method of treating water or wastewater which involves first a facultative anaerobic process to degrade solids, break down complex compounds and produce simpler forms of P and N compounds, primarily phosphate and ammonia, as well as volatile fatty acids (xe2x80x9cVFA""sxe2x80x9d). The VFA""s are then contacted with a P-removal microbial consortia which uptakes and stores the VFA""s anaerobically. The effluent is then passed to a nitrogen removal step where nitrate and ammonia are removed in an anoxic denitrification/aerobic nitrification bioreactor. As well, BOD may be substantially reduced at this stage. The effluent then returns to the P-removal bioreactor for aerobic phosphate removal. The effluent is now substantially free of N and P compounds as well as being substantially free of SS and BOD.
Therefore, in one aspect of the invention, the invention comprises a process of treating liquid contaminated with organic, BOD, COD, N containing and/or P containing compounds, said process comprising the steps of:
(a) passing the liquid through a P-removal bioreactor comprising an immobilized microbial consortia which are charged or recharged with a carbon source present in the liquid;
(b) passing the effluent from step (a) through the P-removal bioreactor which has been charged or recharged from step (a) under conditions which allow the microbial consortia to uptake and store P compounds;
(c) removing the wastewater from the P-removal bioreactor and providing a P-release solution effective to cause the microbial consortia to release the P previously stored; and
(d) removing the P-release solution containing the released P from the P-removal bioreactor.
In one embodiment, the process of claim 1 further comprising the step of passing the liquid through an anaerobic bioreactor comprising an immobilized microbial consortia which degrade organic components in the liquid and produce volatile fatty acids which serves as the carbon source. The process may further comprise the step of passing the effluent from the P-removal bioreactor through at least one other bioreactor comprising an immobilized microbial consortia for at least partially removing N containing compounds, BOD and/or COD from the wastewater. The at least one other bioreactor may comprise a nitrogen removal bioreactor comprising a denitrification zone comprising microbial consortia which convert nitrogen oxides into nitrogen gas and a nitrification zone comprising microbial consortia which convert ammonia into nitrogen oxides.
The at least one other bioreactor may further comprise an aerobic BOD removal bioreactor and/or an aerobic polishing bioreactor wherein residual ammonia and/or suspended solids are further polished out.
In one preferred embodiment, there are at least two P-removal bioreactors used alternately such that while one is being charged or recharged with effluent from the anaerobic bioreactor, one other is being used to treat effluent from the nitrogen removal bioreactor. More preferably, there are three P-removal bioreactors used alternately in a continuous fashion such that while one is being charged or recharged with effluent from the anaerobic bioreactor, a second is being used to treat effluent from the nitrogen removal bioreactor and the third is being treated with the P-release agent.
In another embodiment, the process further comprises a step of passing at least a portion of the effluent from the anaerobic bioreactor through a strictly anaerobic bioreactor comprising an immobilized methanogenic microbial consortia which metabolize the VFA""s and produce methane.
In another aspect of the invention, the invention comprises a process of treating wastewater containing biodegradable suspended solids and/or organic compounds, said process comprising the steps of:
(a) passing the wastewater through a facultative anaerobic bioreactor comprising a microbial consortia which produces hydrolyzing enzymes which breakdown the solids and/or organic compounds in the wastewater and which produce volatile fatty acids as a result of facultative anaerobic processes; and
(b) passing at least a portion of the effluent from the facultative anaerobic bioreactor through a strictly anaerobic bioreactor comprising a methanogenic microbial consortia.
In one embodiment, the process does not include any step of settling and removing solids from the wastewater prior to step (a). The effluent from the strictly anaerobic bioreactor may be further treated to remove one of or a combination of any of the following: P-containing compounds, N-containing compounds, BOD, COD and/or suspended solids.
In another aspect of the invention, the invention comprises a nitrogen removal bioreactor apparatus comprising:
(a) an anoxic denitrification bioreactor having a liquid inlet, a liquid outlet and a gas outlet and comprising a microbial consortia which reduces nitrogen oxides to nitrogen gas;
(b) an aerobic nitrification bioreactor having an inlet and an outlet and comprising a microbial consortia which oxidizes ammonia to nitrogen oxides;
(c) means for connecting the outlet of the denitrification bioreactor to the inlet of the nitrification bioreactor for transferring liquid from the denitrification bioreactor to the nitrification bioreactor; and
(d) means for recycling at least a portion of effluent from the outlet of the nitrification bioreactor to the inlet of the denitrification bioreactor.
In one embodiment, the apparatus may further comprise means for aerating or oxygenating the nitrification bioreactor. The connecting means may comprise a system which transfers liquid from the denitrification bioreactor to the nitrification bioreactor when the liquid reaches a predetermined level within the denitrification bioreactor. The transfer system may proportionally slows down the rate of liquid transfer as the liquid level within the denitrification bioreactor is reduced. The connecting means may preferably be a siphon system which is gravity operated.
In one embodiment, the denitrification bioreactor is a substantially cylindrical container and the nitrification bioreactor is an annular container which surrounds the denitrification bioreactor. Flow within the denitrification bioreactor is preferably non-plug flow.
In yet another aspect of the invention, the invention comprises an integrated unitary bioreactor for removing organic solids, BOD and/or nitrogen compounds from a wastewater stream, comprising:
(a) an anaerobic fermentation chamber comprising immobilized facultative anaerobic microbes and having an inlet and an outlet;
(b) a combined BOD/nitrogen removal chamber comprising a first microbial population of heterotrophic aerobic microbes, a second population of aerobic nitrifying microbes and a third population of anoxic dentrifying microbes and having an inlet connected to the anaerobic chamber outlet and an outlet;
wherein the mixture of the first, second and third populations of microbes adjusts in response to the relative level of BOD, nitrates and ammonia introduced into the BOD/nitrogen removal chamber.
In one embodiment, the bioreactor further comprises an gas dissolving system for introducing oxygen into the BOD/nitrogen removal chamber such that an upper portion of said chamber is aerobic. The gas dissolving system may also introduce ozone into the BOD/nitrogen removal chamber.
In one embodiment, the first and second populations of microbes dominate an upper portion of the BOD/nitrogen removal chamber and the third population dominates a lower portion of said chamber. The effluent from the anaerobic chamber may be introduced into the lower portion of the BOD/nitrogen removal chamber.
In one embodiment, the bioreactor further comprises a siphon system which draws liquid from the BOD/nitrogen removal chamber to an effluent chamber and a liquid recycling system which draws liquid from the effluent chamber and distributes it at the top of the BOD/nitrogen chamber. The liquid level in the effluent chamber may be controlled by a level controller and a pump which pumps liquid to a discharge or back to the BOD/nitrogen chamber.